The present invention relates generally to optical communications and more particularly to K-alternate channel selection for the routing, wavelength assignment and spectrum allocation in flexible optical WDM networks.
The channel spacing in the current optical WDM networks is fixed and same for all channels, standardized by the ITU-T [ITU-T], irrespective of the line rate of channels (FIG. 1(a)). We refer to such networks as the fixed grid networks. Fixed spectrum assigned to channels in the fixed grid networks may not be sufficient if the channels require larger spectral width to support higher line rates. On the other hand, if channels are operating at low line rates, then the required spectrum may be smaller than the assigned spectrum. Thus, in a mixed line rate system, the spectrum efficiency is not optimized for each line rate in the fixed grid networks.
There has been growing research interests on optical WDM systems that are not limited to fixed ITU-T channel grid, but offer flexible channel grid to increase the spectral efficiency. We refer to such networks as the Flexible optical WDM networks (FWDM) (FIG. 1(b)).
Some important problems in the FWDM networks are: for a given configuration of the optical network in terms of location of optical nodes and the deployed fibers connecting optical nodes, and a given set of connections with finite data rates between two disjoint optical nodes; i) how to find a set of all-optical channels (channels that are distinguished based on its operating wavelength and spectrum allocation) which can support the requested data rate for each connection; ii) how to select the line rate of channels for each connection to support the required data rates; and iii) how to route these channel in the network, such that the total required spectrum for the optical WDM network is minimized. Channels which transfer data between end users, without converting them into electrical domain, are referred to as the All-Optical channels. Together the problems described above are referred to as the Routing, Wavelength assignment, and Spectrum Allocation (RWSA herein) in the all-optical flexible optical WDM networks.
Since in the fixed grid networks, the spectrum, assigned to each channel, are fixed and remain the same for all channels, the channels can only be distinguished based on their operating wavelength. Thus, the RWSA problem is transformed into the Routing, and Wavelength Assignment problem (RWA). The RWA is the special case of the RWSA problem in which the spectral width of all channels is the same. When finding a connection in all-optical fixed grid WDM networks using the RWA solutions, we need to make sure that the same wavelength is available on all fiber cables along the route, which we refer as the wavelength continuity constraint. On the other hand, when finding a connection in the FWDM networks, the RWSA solutions need to satisfy not only the wavelength continuity constraint, but also make sure that the same continuous spectrum is available on each fiber in the link, which we refer as the spectral continuity constraint. Additionally, the spectrum allocation to different channels must be non-overlapping, which we refer as spectral conflict constraint. Thus, due to spectral continuity and spectral conflict constraints, existing solutions for the RWA problem may not be applicable to the RWSA problem.
We have proposed a mathematical formulation of the problem in terms of Integer Linear Program (ILP). However, the time required to solve the RWSA problem using the ILP is very long, and increases exponentially with the system size. Thus, the contemplated solution is not scalable.
Accordingly, there is a need for an efficient channel selection in a flexible WDM (FWDM) network.